The battleground pollsters are fortunate that President Obama won by such a comfortable margin in 2008. Otherwise they would have had some explaining to do. The Real Clear Politics average incorrectly predicted the 2008 outcomes in Indiana and North Carolina, although the margins were close. More significantly, the averages in New Mexico, Iowa, and Nevada were off by six points or more. In three other states, Colorado, Pennsylvania, and Michigan, the averages were off by at least three points.

The final 2008 RCP national average predicted a 7.6-point victory for Obama — a remarkably accurate prediction (Obama’s actual margin was 7.3 points). Unlike the state polls, the national polls were consistent in showing Obama with a comfortable lead throughout October.

Similarly in 2004, the RCP national average was only off by about a point. The state averages were also fairly accurate, with one exception: Florida. RCP predicted a very narrow 0.6 percent victory for George W. Bush in the Sunshine State. His actual margin of victory was a relatively solid five points. If the RCP average had been closer to the actual five-point margin of victory, Bush would have been a much stronger favorite to win heading into the election.

Unlike in 2004, when the inaccuracies in the state polls seemed to affect both candidates evenly, in 2008 the polls understated President Obama’s margin of victory in 10 of the 13 battleground states. The most likely cause for the difference is the strength of Obama’s ground campaign, which outperformed McCain’s effort by leaps and bounds.

The accuracy of state polling is particularly crucial this year because so many states are hotly contested. According to the RCP state averages, right now the candidates are within three points of each other in eight states: Florida, New Hampshire, Colorado, Virginia, Ohio, Iowa, Wisconsin, and Nevada. These states have 95 electoral votes — enough to put either candidate over the top.

Brandon J. Gaylord, the editor-in-chief ofHorseRacePolitics.com, is a graduate of George Washington University’s Graduate School of Political Management. Brandon got his start in politics as an intern in Vice President Richard Cheney’s Office of Political Affairs. You can contact Brandon at [email protected].